Methods for increasing germanium concentration of surfaces of a silicon germanium portion of a Fin and resulting semiconductor devices

Abstract

In an embodiment, a device includes a substrate, a first semiconductor layer that extends from the substrate, and a second semiconductor layer on the first semiconductor layer. The first semiconductor layer includes silicon and the second semiconductor layer includes silicon germanium, with edge portions of the second semiconductor layer having a first germanium concentration, a center portion of the second semiconductor layer having a second germanium concentration, and the second germanium concentration being less than the first germanium concentration. The device also includes a gate stack on the second semiconductor layer, lightly doped source/drain regions in the second semiconductor layer, and source and drain regions extending into the lightly doped source/drain regions.

What is claimed is: 
     
       1. A method comprising:
 forming a fin that protrudes from a substrate, a top portion of the fin comprising a first semiconductor material, wherein a bottom portion of the fin and the substrate comprise a second semiconductor material different from the first semiconductor material; and 
 exposing a top surface and sidewalls of the top portion of the fin to a hydrogen plasma, wherein after exposing the top surface and the sidewalls of the top portion of the fin to the hydrogen plasma, a germanium concentration increases in a direction extending from a center portion of the top portion of the fin to edge portions of the top portion of the fin. 
 
     
     
       2. The method of  claim 1 , wherein after forming the fin, a width of the top portion of the fin and a width of the bottom portion of the fin are equal, and after exposing the top surface and the sidewalls of the top portion of the fin to the hydrogen plasma, a first width of the top portion of the fin and a second width of the bottom portion of the fin are different. 
     
     
       3. The method of  claim 2 , wherein the first width is smaller than the second width. 
     
     
       4. The method of  claim 1 , wherein the first semiconductor material comprises silicon germanium, and the second semiconductor material comprises silicon. 
     
     
       5. The method of  claim 1 , wherein exposing the top surface and the sidewalls of the top portion of the fin to the hydrogen plasma comprises:
 generating a plasma from hydrogen (H 2 ) and argon (Ar) gases in an etch chamber; and 
 exposing the top surface and the sidewalls of the top portion of the fin to the plasma to form silane (SiH 4 ) and germane (GeH 4 ) gases. 
 
     
     
       6. The method of  claim 1 , further comprising:
 before exposing the top surface and the sidewalls of the top portion of the fin to the hydrogen plasma, forming an isolation region around the fin. 
 
     
     
       7. The method of  claim 1 , further comprising:
 after exposing the top surface and the sidewalls of the top portion of the fin to the hydrogen plasma, forming an isolation region around the fin. 
 
     
     
       8. A method comprising:
 forming a first semiconductor layer over a substrate, the first semiconductor layer comprising a first material that is different from a second material of the substrate; 
 etching trenches into the first semiconductor layer and the substrate to form a fin, wherein the fin includes a top portion that comprises the first material, and a bottom portion that comprises the second material, wherein edges of the top portion of the fin have a first germanium concentration; and 
 performing a hydrogen radical treatment process on the edges of the top portion of the fin, wherein after performing the hydrogen radical treatment process, a second germanium concentration of the edges of the top portion of the fin is greater than the first germanium concentration, wherein a difference between the second germanium concentration and the first germanium concentration is in a range from 4 percent to 6 percent. 
 
     
     
       9. The method of  claim 8 , wherein the hydrogen radical treatment process is performed at a pressure that is in a range from 0.1 Torr to 6 Torr. 
     
     
       10. The method of  claim 8 , wherein the hydrogen radical treatment process is performed at a temperature that is in a range from 100° C. to about 600° C. 
     
     
       11. The method of  claim 8 , wherein the first semiconductor layer comprises silicon germanium, and performing the hydrogen radical treatment process further comprises simultaneously removing silicon and germanium from the edges of the top portion of the fin. 
     
     
       12. The method of  claim 11 , wherein after performing the hydrogen radical treatment process, a first width of the top portion of the fin is smaller than a second width of the bottom portion of the fin. 
     
     
       13. The method of  claim 11 , wherein performing the hydrogen radical treatment process further comprises removing the silicon from the edges of the top portion of the fin at a first rate, and removing the germanium from the edges of the top portion of the fin at a second rate, wherein the first rate and the second rate are different. 
     
     
       14. The method of  claim 13 , wherein the first rate is greater than the second rate. 
     
     
       15. A method comprising:
 growing a first semiconductor layer over a substrate; 
 forming a semiconductor strip by etching trenches that extend through the first semiconductor layer and partially through the substrate; 
 forming a dummy gate stack on a top surface and sidewalls of the semiconductor strip; 
 forming gate spacers on sidewalls of the dummy gate stack; 
 depositing an inter-layer dielectric to surround the gate spacers and the dummy gate stack; 
 removing the dummy gate stack to form a recess that exposes the top surface and the sidewalls of the semiconductor strip; and 
 performing a hydrogen radical treatment process on the exposed top surface and the sidewalls of the semiconductor strip in the recess. 
 
     
     
       16. The method of  claim 15 , wherein after performing the hydrogen radical treatment process, a top surface of the semiconductor strip in the recess is below bottom surfaces of the gate spacers. 
     
     
       17. The method of  claim 15 , wherein after performing the hydrogen radical treatment process, a first width of the semiconductor strip exposed by the recess is smaller than a second width of the semiconductor strip that is beneath the gate spacers. 
     
     
       18. The method of  claim 15 , wherein the first semiconductor layer comprises silicon germanium, and the substrate comprises silicon. 
     
     
       19. The method of  claim 18 , wherein performing the hydrogen radical treatment process comprises:
 exposing the top surface and the sidewalls of the semiconductor strip in the recess to a hydrogen radical, the hydrogen radical reacting with silicon of the semiconductor strip to form silane at a first rate, the hydrogen radical reacting with germanium of the semiconductor strip to form germane at a second rate, wherein the second rate is lower than the first rate. 
 
     
     
       20. The method of  claim 8 , wherein the hydrogen radical treatment process is performed for a time span of less than 100 seconds.